In English one can write either of these to indicate a height difference:
Marcus is taller than Gaius by a head.
Marcus is a head taller than Gaius.
I am looking for an idiomatic way to translate "by a head" in this context. I found good adjectives for "tall" in my previous question. A simple start is to drop the measure and write simply:
Marcus procerior est quam Gaius.
Marcus Gaio procerior est.
To indicate by how much someone is taller than someone else, one should use an ablative of measure (ablativus mensurae). That is, tribus metris longior and chiliogrammate gravius are the correct ways to say "three meters longer" or "a kilogram heavier". In this case, this approach leads me to these:
Marcus capite procerior est quam Gaius.
Marcus Gaio capite procerior est.
I am not sure if these would be parsed correctly and especially if this would be idiomatic classical Latin. One could read capite as an ablative of respect (ablativus respectus), leading to the interpretation that Marcus has a taller head than Gaius. This is not what I want to say.
Perhaps one could clarify "by a head" to "by the length/height of a head". I could use mensura or altitudo to produce:
Marcus mensura capitis procerior est quam Gaius.
Marcus Gaio altitudine capitis procerior est.
This is my best guess. How should I translate "by a head" in this context? I prefer classical Latin, but I do not require it.